The present invention relates to electronic flashers for vehicles. More particularly, the present invention relates to a combination automobile flasher wherein flash rates and duty cycles are tightly controlled to provide a means of alerting a driver to lamp outage while satisfying motor vehicle regulations.
The U.S. Department of Transportation has promulgated Federal Motor Vehicle Safety Standards which require both turn signal and hazard warning flashers to operate within a specific range of flashes per minute and duty cycles. The Safety Standards also require a "significant change" in flash rate upon the outage of one or more lamps in the turn signal mode. The hazard warning flasher must operate at the same speed regardless of the number of operational lamps in order to maximize the visual perception of the flashing lamps.
Flashers can be of the thermal type, where a metal strip acts with a heater wire and ribbon to open and close a contact at a set interval or of the electronic type, wherein a capacitor and a resistor act together to turn the flasher "on" and "off." To satisfy the "significant change" requirement, thermal flashers usually operate in a "steady on " condition and electronic flashers double in flash rate when a lamp is lost in turn signal mode. In the past, automobile flasher systems have been constructed with two separate flashers. In these prior art systems, one flasher operates the automobile signal lamps in turn signal mode and the other flasher operates the lamps in hazard warning mode.
Automobile manufacturers have recently begun using combination flashers whereby one electronic flasher provides both turn and hazard warning signals. The units are designed to double in flash rate in order to indicate a lamp out in the turn signal mode. While the combination flasher saves space and cost, a conflict with the Safety Standards can arise when a combination flasher is used with a 6-lamp system in which three lamps on each side of the vehicle act as turn indicators. For example, in a 6-lamp system, if one or more lamps are lost on either side of the vehicle, the flash rate will double in the turn signal mode on that side. The hazard warning signal remains at the slower flash rate as required by the Safety Standards. However, in the event of a 4-lamp failure, the combination flasher will operate at a double flash rate in hazard warning mode because the combination flasher detects only a 2-lamp load. Because such an occurrence could cause a hazard warning flash rate and duty cycle outside the allowable limits, the condition would amount to a violation of the Safety Standards.
One solution to the forgoing problem is to add a terminal to the flasher that would indicate whether the vehicle is in turn signal or hazard warning mode. A special integrated circuit would be designed to monitor this terminal, and adjust the flash rate accordingly. While solving the problem, this solution is impractical since it would require an additional terminal on the flasher, an additional plug and wiring, and a new switch design.
There is a need therefore, for a combination flasher wherein the flash and duty cycles can be so tightly controlled that a significant change can be had in the flash rate while still meeting Federal Safety Regulations.